Passive stabilization tanks

ABSTRACT

The present invention consists in a passive stabilizing tank installation for damping components in the movement of a floating body, comprising two partially filled tanks which are connected by ducts for the passage of liquid and of air above the liquid in the tanks, between the tanks, the ducts being provided with frequency regulating duct means with a regulating device in the form of a slide or rotary valve with a full plate and bypass duct means, a second regulating valve in the form of a plate or slide with an opening being provided for adjusting the natural tank damping, both in the regulating duct means and also in the bypass duct means or in at least one duct serving for air movement between the tanks.

United States Patent Csupor [54] PASSIVE STABILIZATION TANKS [72] Inventor: Denis I). A. Csupor, Geneva, Switzerland [73] Assignee: Maierform Holding S.A., Geneva, Switzerland [22] Filed: June 30, 1970 [211 App]. No.: 51,316

[52] U.S.Cl ..ll4/l25 [51] Int. Cl ...B63b 43/06 [58] Field of Search ..l l4/l25 [56] References Cited UNITED STATES PATENTS 3,487,801 1/1970 Calvi ..ll4/l25 FOREIGN PATENTS OR APPLICATIONS W 15 QOP-Y [451 July 25, 1972 996.070 6/1965 Great Britain ..l 14/125 Primary Examiner-Trygve M. Blix Attorney-John Lezdey [5 7] ABSTRACT The present invention consists in a passive stabilizing tank installation for damping components in the movement of a floating body, comprising two partially filled tanks which are connected by ducts for the passage of liquid and of air above the liquid in the tanks, between the tanks, the ducts being provided with frequency regulating duct means with a regulating device in the form of a slide or rotary valve with a full plate and bypass duct means, a second regulating valve in the form of a plate or slide with an opening being provided for adjusting the natural tank damping, both in the regulating duct meansand also in the bypass duct means or in at least one duct serving for air movement between the tanks.

1 I Claims, 14 Drawing Figures Patented July 25,1972 BEST AVAILABLE COP-Y 3.618.877

4 Shuts-Slut 1 INVENTOR:

DENIS D. A CSUPOR Patented July 25, 1972 BEST AVAILABLE COPY 3,678,877

4 Shuts-Shut 8 INVENTORI .DENIS D. A. CSUPOR Pmmd Jul 25, 1972 BEST AVALLABLE'GOPY 3,678,877

4 Shuts-Slut 5 INVENTOR:

DENIS I). A. CSUPOR Patented July 25, 1972 BEST AVAEABLE GQPY 3,678,877

4 Shuts-Shut 4 INVENTOR:

DENIS D.A. CSUPOR PASSIVE STABILIZATION TANKS BACKGROUND OF INVENTION 1. Field to which invention relates The present invention relates to passive stabilization tanks and more particularly to such tanks for the damping of periodic movements of a floating body caused by the movement of the sea, such as the rolling movements of a ship, and comprising two partially filled lateral tanks, which are connected by ducts for the passage of the liquid contained in the tanks and the air above the liquid on movement of .the tanks, the duct system for the movement of the liquid comprising a regulating channel with a frequency regulating device which is constructed in the form of a slide, or a rotary valve part in the form of a full plate and at least one bypass duct connected in parallel.

2. The prior art Stabilizing tanks have been known for a considerable time in naval architecture; the classical U-tank or Frahm tank (H. Frahm: Neuartige Schlingertanks zur Abdiimpfung von Schiffsvollbewegungen und ihre erfolgreiche Anwendung in der Praxis," J.S.T.G. Hamburg 1911, pages 283 to 365) comprises two lateral tanks partially filled with liquid, which in their lower part are connected by a liquid duct while in their upper part they are connected by an airduct. When the height of the liquid duct is greater than the height of the liquid level, one and the same duct is used both as a liquid duct and also as an air duct one speaks of a tank with an open transverse duct (1. Vasta, A.l. Giddings, A. Talpin, I.l. Stilwell: Roll stabilization by Means of passive Tanks. T.S.N.A.M.E. Volume 69, New York, 1961, pages 411 to 438).

It has also been established (see Article by l.H. Chadwick and K. Klotter: On the Dynamics of Anti-Roll Tanks. Schiffstechnik", 8th issue, February 1955, 2nd volume, Hamburg, pages 85 to 104, and 6.1. Goodrich: Development and Design of Passive Roll Stabilizers," T.R.I.N.A., London, 1969, pages 81 to 95) that the stabilizing tank only operates satisfactorily when its natural frequency is the same in value as the natural frequency of roll of the ship or, in the case of completely regular excitement (in the case of sailing over regulars swell), when the natural tank frequency agree with the frequency with which the ship meets waves. It has also been established that the natural damping effect of the stabilizing tank has a considerable influence on the stabilizing effeet. A low natural damping is favorable in the case of a regular sea, if the natural tank frequency is matched to suit the exciting frequency. A medium natural frequency is more favorable in the case of sailing in an irregular sea when the natural tank frequency is matched to suit the natural frequency of the sea.

In the case of a very high degree of damping the roll damping effect of the stabilizing tank is considerably less.

The optimal natural frequency and the optimal natural damping can .be determined for each particular case of loading of the ship on the basis of model tests or on a basis of theoretical considerations. The favorable values can also be determined by trials, if suitable regulating possibilities and measuring instruments are available.

The regulation of frequency necessary for achieving optimum results has up till now been obtained by changing the cross-section of the liquid duct between the lateral tanks, so that the effective reduced swinging length is rechanged, if the surface of the lateral tank is constant or held approximately constant, while, however, the passage cross-section is changed over a considerable length, the swinging effect and thus also the frequency is changed. The simplest case is when the crosssection is narrowed or broadened out over a long path in the liquid duct; all previous proposals for a change in frequency for purposes of regulation originate from this principle.

Thus there has been a proposal (see German Pat. No. l 1 53,283) to reduce the cross-section by the use of two plates held as an angle to each other in the manner of a roof with a variable gable height. This installation has little frequency cffeet in the case of very high damping influence, as has been proved recently by investigations on triangular shaped restrictions (Volpich: Neue Untersuchungen iiber Schlingertank- Anlagen, J.S.T.G., vol. 62, Hamburg, pages 205 to 227, 1968).

Furthermore an attempt has been made (see German Pat. specification No. 1,262,812) to construct the upper part of the liquid duct, together with the inner walls of the lateral tanks so as to allow for vertical adjustment.

In the case of these known devices the regulating parts are extraordinarily large. Furthermore there are problems as regards sealing and mechanical construction; the displacing forces are very large. This leads to such installations being heavy, expensive and difficult to operate.

The liquid duct canalso be divided up by the bottom flanges of the double bottom into a number of individual ducts (Blohm & Voss brochure Schiffsstabilsierungsanlagen" Hamburg, 1968), in which case each duct contains its own separate valve and the valves are all closed or opened in unison or the valves can be opened separately. In this manner a six-stage regulation in frequency with six ducts and six individual valves is possible. The valve parts or flaps are arranged on three setting shafts. This installation requires the arrangement of several setting mechanisms and was apparently only designed for staggered setting.

In the case of a known tank with an open transverse duct the liquid cross-section changes with the level height, so that in the case of this type of the tank the frequency can be changed by changing the level. The disadvantage of this feature is that the change in the level with respect to a mean optimum setting involves a loss in stabilizing capacity, since in the case of a sinking level the quantity of water available or in the case of a raising of the level of the free space is limited which can be taken up as the masses of water flow from one side to the other.

lt has further been established that the blocking valves which were used by Frahm (H. Frahm: Neuartige Schlingertanks zur Abdarnpfung von Schiffsvollbewegungen und ihre erfolgreiche Anwendung in der Praxis," J.S.T.G., Hamburg 1911) in the air duct considerably increase the natural damping when they are in the partially opened condition. However, such substantial increases in damping is accompanied by a change in the natural frequency.

Finally a stabilizing tank with several connecting ducts between the side tanks being proposed (British Pat. specification No. 1,006,036) in which in one of the connecting ducts a slide or rotary valve is provided. ln the case of this known stabilizing tank, however, just as is the case with all other known adjustable stabiling tanks, natural frequency and natural damping are inflexibly connected together. The operation characteristic of this known stabilizing tank can thus be indicated by a single curve, which indicates the relationship between the frequency set and the natural damping.

SUMMARY OF INVENTION On the other hand one aim of the invention is to provide a stabilizing tank of the above-mentioned type in which the natural frequency and the natural damping can be regulated substantially independently of one another over a wide range.

The present invention consists in a passive stabilizing tank installation for damping components in the movement of a floating body, comprising two partially filled tanks which are connected by ducts for the tanks, between the tanks, the ducts being provided with frequency regulating duct means with a regulating device in the form of a slide or rotary valve with a full plate and bypass duct means, a second regulating valve in the form of a plate or slide with an opening being provided for adjusting the natural tank damping, both in the regulating duct means and also in the bypass duct means or in at least one duct serving for air movement between the tanks.

On the basis of this construction the lateral frequency can be changed over a wide range for example 40 to percent without the natural damping increasing to an extreme value. (The term good frequency regulation is to be taken to mean such a regulation in which'the damping increases by approximately the same percentage as the frequency); with the construction in accordance with the invention it is also, however, possible to change the natural damping over a wide range, preferably by more than 100 percent and in extreme cases for up to 500 percent, without the natural frequency being influenced substantially, for instance more than I to 6 percent.

In accordance'with the invention it is also possible to match the frequency by the frequency regulating means and consequently set the damping to an optimum value without the change in frequency connected with the setting ofthe damping means making it necessary to undertake a correction in the frequency by means of the frequency regulating means after the setting of the damping action. The invention thus provides an easily manipulated rapidly adjustable regulating means for the natural frequency and the natural damping of a ship, the upper and the lower limit of the frequency and the damping regulation being determined by the requirements which arise owing to the extreme conditions of loading of the ship in operation. The construction in accordance with the invention thus fulfills the important requirement that the adjustment can be undertaken rapidly, it being possible to carry out subsequent adjustment by feel" or by means of instruments taking standard settings as a basis.

In accordance with a preferred embodiment of the invention the regulating duct and the bypass duct or ducts constitute a constructional unit, in which they are separated from each other by a transverse partition or partitions. This form of construction has certain advantages from the point of view of shipbuilding construction.

A further embodiment of the invention has the feature that the inlets and outlets of the regulating duct and the bypass duct or ducts lie below the liquid level in the lateral tanks. The arrangement can, however, be such that the regulating duct is arranged above the bypass duct and in accordance with the height is above the liquid level in the lateral tanks, so that in the regulating duct a free liquid surface is formed, while the bypass duct is completely filled or immersed.

A further embodiment of the invention is so constructed that the regulating duct and the bypass duct or the regulating duct and the bypass ducts are adjacent to one another and in height are above the liquidlevel in the lateral tanks so that the liquid forms a free surface in all liquid ducts.

The lengthof the bypass duct or ducts is preferably greater than the length of the regulating duct so that its or their exits or outlets extend into the lateral tanks.

The plate with an opening is preferably comblike or reticular, grid-like or perforated. Although there has been a previous proposal to provide a passive tank stabilizing installation (see British Pat. specification No. 1,002,788) in which rotary valve flaps are provided between two lateral tanks and a cen-v tral tank, in the open condition these valve flaps have several elongated openings or passages while in the close condition they practically form a solid wall. The valve flaps of the known arrangement therefore do not constitute damping devices but serve to block or free the passage to the lateral tanks.

A further particularly convenient form of construction in accordance with the invention is characterized in that the bypass duct or ducts is or are of the closed type lying under the liquid level and the regulating duct has the form of an intermediate tank, which is arranged between the two inner walls of the lateral tanks and is connected with the lateral tanks by respective openings, the passage being capable of being regulated by these openings using a frequency regulating flap or a frequency regulating slide. However, it is also possible for the intermediate tank used as a regulating duct to be divided up by one or more longitudinal partitions, preferably in the longitudinal direction of the ship, the longitudinal partitions also preferably being provided with a transverse flow opening and a frequency regulating flap or slide is provided in at least one of these openings. The intermediate tank is preferably completely filled with liquid so that the liquid level lies higher than the liquid level in the side tanks. In the case of a previously proposed stabilizing device for floating bodies (see German Pat. specification No. 1,268,998) openings with sliding doors are provided between the different tank parts. By operation of these sliding doors it is, however, only possible to bring about a throttling of the passage transversely through the tank. The known devices do not have or make use of the additional closed ducts in accordance with the invention, which connect the two lateral tanks. A true frequency regulation, that is to say a regulation of frequency which only has an insubstantial effect upon the damping action, is not possible with the previously proposed stabilizing equipment. v

The above-mentioned constructions can be used with particular advantage in giant tankers by using the cargo tanks of parts of the ship as a stabilizing tank installation.

In accordance with a further preferred construction in accordance with the invention frequency regulating devices constructed in the form of a rotary valve or flap and the damping regulating devices are so mounted on a common axis of rotation that the two planes, in which the frequency valve and the damping valve lie, are set at an angle of substantially in relation to each other. Since the stabilizing tank installation in accordance with the invention has a large range of regulation as regards frequency and damping it is sufficient if it is installed togetherv with one, or more other stabilizing tanks which cannot be requlated on board a ship or other floating body and the regulation of the overall action of all tanks is carried out using only the one stabilizing tank installation which is constructed so as to be capable of regulation.

LIST OF SEVERAL VIEWS OF DRAWINGS The invention is now described in what follows by way of example with reference to the accompanying drawings.

FIG. 1 is a diagrammatic cross section of stabilizing tank construction intended only for regulation of frequency.

FIG. 2 is a longitudinal cross section of the construction shown in FIG. 1.

FIG. 3a is a diagrammatic cross section through a stabilizing tank construction in accordance with the invention making possible, a substantially independent adjustment of frequency and damping.

FIG. 3b is a diagrammatic longitudinal section of the construction shown in FIG. 3a. I

FIGS. 4 and 5 are diagrammatic cross sections of further embodiments of a damping regulating system in accordance with the invention.

FIG. 6a is a diagrammatic cross section through a further construction of a stabilizing tank installation in accordance with the invention.

FIG. 6b is a diagrammatic longitudinal section of the construction shown in FIG. 6a.

FIG. 7 is a diagrammatic plan view of a further embodiment of a stabilizing tank installation in accordance with the invention.

FIG. 8a is a diagrammatic cross section of a further embodiment of a stabilizing tank installation in accordance with the invention.

FIG. 8b is a diagrammatic plan view of the construction in accordance with FIG. 8a.

FIG. 9a is a diagrammatic longitudinal view of a further construction of a stabilizing tank installation in accordance with the invention. 1

FIG. 9b shows the same cross section as in FIG. 9a in which, however, the dampingand frequency regulating valves are set at 90 in relation to each other.

FIG. 90 shows a diagrammatic section of the construction in accordance with FIG. 9b.

DESCRIPTION OF PREFERRED EMBODIMENTS The stabilizing tank construction shown in FIGS. 1 and 2 includes the lateral tank 1, 2, which are connected with each other for the passage of liquid by a connecting duct 14 at the lower end. At the upper end an air connecting duct 13 is provided.

The lateral tanks 1, 2 are filled to such an extent that the liquid levels 1 l, 12 are above the level of the connecting duct 14.

The liquid duct 14 is divided in the simplest case as shown in FIGS. 1 and 2 by a longitudinally extending intermediate wall or partition 3. One of the two parts divided oil by the partition, that is to say the regulating duct 4, has a slide 5 mounted in it, while the other part is left unobstructed as a bypass duct 6. When the slide is drawn upwards or swing upwards, the tank in accordance with FIG. 1 behaves substantially as a classical tank without internal obstructions. However, if the slide 5 in the regulating duct is closed to a certain extent, the coefficient of resistance in the regulating duct per meter of duct breadth is increased with respect to the corresponding coefficient in the bypass duct.

Since in the duct 14 the speeds of flow obtaining are much higher than in the lateral tanks 1, 2, the overall inertia of the stabilizing tank installation is mainly determined by the cross section of the duct 14, so that the increase in inertia in the duct in the above-described manner involves considerable changes in frequency. If the duct for example is divided in accordance with the invention so that the regulating duct makes up three quarters of the whole duct width and the bypass duct makes up one quarter of it, the kinetic energy and thus the inertia of the overall system is increased four-fold when the slide 5 is closed. This means a proportional change in the natural frequency of approximately 100 percent.

With the help of the slide 5 in the regulating duct 4 it is also possible to set all intermediate values of the tank frequency with regulating settings between the open and closed condition of the slide steplessly. In this respect the resistance of the slide 5 not only brings about a loss in energy, but also, on the contrary, has the primary effect of changing the frequency. The resistance to flow of the slide 5 naturally also exerts a certain effect on the damping action. This effect is, however, incomparably smaller than will be the case when the duct is not divided and theslide is continuous. It is therefore important that the slide only extends across part of the duct, that is to say that part inwhich the speed is considerably reduced as compared with the mean flow speed in the case of the regulating setting of the slide. With a decrease in the speed damping, however, is reduced in accordance with a square function.

The natural damping is admittedly changed to a limited extent in accordance with the frequency setting; it however always remains between the two limits which are constituted by the open and closed conditions of the regulating duct.

The arrangement shown in FIGS. 1 and 2 thus constitutes a frequency regulator, in which in the case of minimum influence on damping the frequency can be rapidly and steplessly adjusted within a wide range. The frequency regulator only requires a single setting mechanism with very small setting forces and only comprises a single slide which can easily be manufactured and mounted in position.

Apart from the action of the unilateral influence on resistance in the duct the slide also has an effect on the frequency owing to its hydrodynamic mass. This hydrodynamic mass is favorable for frequency regulation but, as shown above, is not the only frequency regulating factor, since the frequency regulation in the case of the arrangement in accordance with the invention is brought about by the flow resistance component which otherwise is only disturbing. It is, however, useful to keep the hydrodynamic mass of the slide as large as possible in the case of the arrangement in accordance with the invention.

The frequency regulator, be it a slide or be it a pivoting flap, is preferably in the form of a continuous plate which can, however, be profiled.

The regulation of frequency as described above is used in accordance with the invention together with a substantially frequency independent regulation of damping, something which is now described in what follows with reference to FIGS. 3 to 5. The regulation of damping is achieved in accordance with the invention by the use of a slide 8 passing across the whole duct 14 and having a resistance to flow which is the same for all degrees of closing while, however, its hydrodynamic mass is decreased. The damping regulator in accordance with the invention can be constructed as a grid 15 (FIG. 3b), a comb 16 (FIG. 4) or a perforated plate 17 (FIG. 5) in such a manner that during adjustment its resistance to flow remains while, however, its hydrodynamic mass is reduced. Since slides have a greater hydrodynamic mass than the flap, flaps are preferred to slide for regulation of damping. Slides are more particularly used in those cases when the individual strips of the comb-like slide plates 16 have their axes parallel to the setting direction of the slide.

It is also possible in accordance with the invention to arrange the individual strips of the damping regulating flap l6 behind one another on their own individual axes of rotation instead of a single plane.

In accordance with the invention damping regulators can be incorporated in the liquid duct and in the air duct in the same manner.

FIGS. 3a and 3b show the common arrangement of the frequency regulator 7 and a-damping regulator 8 in the liquid duct 14. The longidutinal partition 3 extends only as far as a position slightly short of the damping regulator 8. The local height of the duct 14 at the position at which the damping regulator 8 is arranged, is denoted by h, the breadth of a plate strip of the damping regulator being denoted by h Preferably the damper in accordance with the invention is so constructed that the frequency difference brought about by it is not greater than 1 percent, at the most 6 percent of the original frequency. This can, however, be achieved by a suitable selection of the number of plate strips located in a plate plane. Ifthe strips in the case of the arrangement of only one damping flap 15 are so small that they would have insufficient mechanical strength, the invention provides the feature of providing several damping flaps with a weaker individual action behind one another and the actuation of the flap by a common setting mechanism.

Similar considerations apply for the comb-like slide 16 in accordance with FIG. 4 and the perforated flap 17 in ac cordance with FIG. 5.

The regulating system in accordance with the invention can be used not only in connection with U-tanks, but also with particular advantage in the case of stabilizing tank installations with a free duct surface in accordance with FIGS. 60 and b. The vertically extending duct 18 is divided up by a horizontal plate 19 into an upper and a lower part 20 and 21 respectively. The upper part 20 is still constructed as a duct with a free surface, while the lower part 21 practically forms the duct of an U-tank. The regulating duct is the upper duct part 20, in which the frequency regulator 9 is arranged.

The damping regulator 10 extends both over the regulating duct 20 and also over the lower covered bypass duct 21. The particular advantage of this arrangement lies in that when the frequency flap 9 is opened, the tank operates as a tank with a free surface, so that it already has a mean natural damping action. When the frequency flap 9 is closed, the tank operates as a pure U-tank is, relatively speaking, less than the natural damping of a tank with a free surface of the same frequency. With theclosing of the frequency flap 9 the frequency is, however, decreased and the passage cross section made narrower, this leading to an increase in natural damping, for example in the case of an U-tank. The change-over in the type of tank from a tank witha free surface to an U-tank has, however, be opposite effect so that in such a tank the natural damping actions in the case of an open and 'a closed frequency flap only differ slightly from each other and if the constructional conditions are suitable it is even possible to ensure that the natural damping is by no means effected by the frequency flap 9. Thus a type of tank is made available in which not only is the damping flap l0 practically devoid of any action of the frequency,

but also the frequency flap 9 has no effect on the damping action. Thus, the effects of the two-regulating elements are completely independent of one another in every respect, this constituting a particularly advantageous arrangement.

If a particularly large range of frequency adjustment is demanded, the arrangement shown in FIG. 7 in plan is particularly advantageous. The liquid duct is, as is the case with the other constructions, divided up into a regulating duct 24 and a bypass duct 22. The two ducts have different lengths when measured in the transverse direction of the ship so that the bypass duct 22 has an extension 25 extending through the inner walls 23 of the lateral tanks 1, 2, with approximately constant cross section, the extension passing into the lateral tanks 1, 2. If in the case of this arrangement the frequency flap is closed, not only is the cross section of the bypass duct increased, but also its length, something which reinforces the reduction in frequency aimed at. It is important in this respect that the basic damping does not undergo any additional increase owing to the extension of the bypass duct when the frequency flap is closed, since the action of a duct on the damping is practically independent of the duct length and substantially is only influenced by the relationship between the cross sections of the duct and the lateral tank. In the case of giant tankers use is frequently made of the cargo tanks of a part of the ship as a stabilizing tank installation. The abovementioned principles can be used with particular advantage inthis respect. FIGS. 8a and b show a tank with two longitudinal partitions 25, which are provided with connecting openings 26 which can be closed in steps by flaps or slides 30. Through these openings 26 the liquid, which in this case is a cargo liquid, can flow through the center tank from one side tank to the other. Furthermore, the two side tanks are connected by one more closed liquid ducts 27 and one or more air ducts 28. When the openings 26 provided in the longitudinal partitions are completely or partially closed, the liquid is compelled to flow partially or completely through the closed ducts 27, which therefore here perform the function of the bypass duct, so that the frequency is reduced with a minimum unintended increase in damping. By connecting the two lateral tanks by means of an air duct 28 the air space 29 is completely enclosed in the center tank part, so that the liquid in this central tank part does not change its mean level during operation of the stabilizing tank, that is to say the center tank 33 only operates as a regulating duct. Therefore, it is possible, without impairing the stabilizing tank action, to fill completely the center tank including the space 29 shown in FIG. 8 so that the cargo volume lost only corresponds to the air spaces in 'the two lateral tanks in the case of this stabilizing tank arrangement.

It is also possible with this arrangement to arrange a damping device in the air duct 28 so that the regulating principle in accordance with the invention can easily be brought into practice in the case of tankers as well and a variation of the arrangements in accordance with the invention is thus constituted.

In accordance with FIGS. 9a to 9c a damping flap 31 and a frequency flap 32 are arranged on a common adjusting shaft so that they lie in mutually perpendicular planes (FIG. 9c). When the frequency flap 32 (FIG. 9a) is closed, the damping flap 31 lies in its neutral position so that it does not influence the damping action in the bypass valve which in this case remains open. If the frequency flap 32 is, however, opened (FIGS. 9b and 90) that is to say if it is set for the highest frequency, the damper is brought by this same rotation of the shaft, which is necessary for opening the frequency flap, is brought into the position of maximum efficiency. This construction does not provide an optimum setting for the damping action but, however, it shows that the damping does not depart from a meanreasonable value in the case of possible frequency settings.

container ships. If in the case of such a ship the stabilizing tank installation is used in such a manner that in the ballast condition it yields good results as regards reduction in rolling, that is to say between 65 and 80 percent, it has been found as a matter of experience that the stabilizing tank installation has a free surface which in the case of laden voyages the metacentric height, which is in any case small, sinks to an impermissible degree as regards static stability or disappears entirely. In such cases the practice has been to use two stabilizing tanks. In the case of a laden voyage with a very high metacenter the two stabilizing tanks are then used while in the case of a laden In the case of the arrangement of stabilizing tanks problems 1 voyage with smaller metacenters only one tank is used.

In accordance with the invention in such cases one of the stabilizing tanks is constructed in accordance with the abovementioned principles for the damping and frequency regulation for the semi-laden, fully laden and intermediate conditions of loading, while, moreover, in order to achieve the stabilizing conditions in the ballast condition, a second tank, which cannot be regulated and which is otherwise used as a conventional ballast tank, is built into a ship. This tank is designed in accordance with the invention fora frequency which is somewhat higher than the highest tank frequency necessary in the case of a ballast voyage and owing to the use of suitable internal fittings increasing resistance it has a medium natural damping action. In the case of a ballast voyage this tank is used as a stabilizing tank. The other tank, designed for a laden voyage, also remains in operation in such a voyage. In the case of this construction both stabilizing tanks have, however, different natural frequencies. The overall action of these two tanks with different natural frequencies can, however, be considered as if the two tanks oscillate or swing with different phases in the case of a certain frequency of roll of the ship. The components of these moments of 0 in phase (cosine or blind components) are added together, just as in the case with the moment components at in phase (sine or cancelling components), in a scalar and form a new resultant moment with a new phase in relation to the movement of the ship. The

apparent common natural frequency of both tanks together results from that frequency at which the sum of the blind components is equal to zero. Since the magnitude of the resultant moment and the resultant phase angle are then added together, if the natural frequency of only one of the stabilizing tanks is changed, the natural frequency of the whole system, and within certain limits also its resultant damping, can be attained by a regulation of only one of the stabilizing tanks. The regulation of this resultant stabilizing action by only one of the two tanks is naturally more restricted than the range of regulation of a single tank which can be regulated. The limited range of regulation for the ballast condition does, however, not involve any disadvantage for regulation, since in accordance with the experience gained with ships, in which these problems exist, the possible metacentric heights and thus also the possible roll frequencies of the ship can only vary within certain limits so that in the case of such ships no very extensive range of regulation is necessary for the ballast condition.

In the case of normal ships whose minimum and maximum metacentric heights have a ratio of l to 2.2 between them, it is sufficient to usea single stabilizing tank which can be regulated in accordance with the invention. The double tank method therefore only needs to be used when in a particular case the metacentric height in the ballast condition exceeds the highest metacentric height in the laden condition for example by a factor of three. The twin tank method with one tank which cannot be regulated and onethat can for example be used with advantage with a type of ship whose metacentric height in the laden condition is 1.10 m while it is 5.50 min the ballast condition.

A particular advantage of the invention consists in the rapid and stepless adjustability of the stabilizing tank in accordance with the invention which makes it possible to set the stabilizing tank without exact information as regards the metacentric height of the ship on the basis of trial and error. Accordingly involved and frequently impossible computing operations are avoided. In this respect the captain can rely on his feel as regards the strength of rolling or the observation of an inclination indicating device. This naturally involves certain errors because conventional inclination indicators installed on ships do not indicate the true but only an imaginary horizon. The arrangement of simple suitable instruments, however, permits a reliable setting which is very close to the optimum. Such a setting is only established when the tank liquid resonates precisely with the movements of the ship, that is to say when the liquid lags behind the movement of the ship for one quarter of a cycle. The establishment of this condition can be detected because when it occurs certain movement magnitudes of the ship and the liquid occur in characteristic phases of the roll movement.

What I claim is:

l. A passive stabilizing tank installation for damping components in the movement of a floating body which comprises at least two tanks for holding a liquid which are connected by ducts for passage of said liquid and of air above the liquid in the tanks; a frequency regulating duct means in one of said ducts for regulating the frequency of the liquid in said tanks, said frequency regulating duct means having a first valve means with a plate, and bypass duct means, having a second valve therein for adjusting natural tank damping whereby when said tanks are partially filled with liquid said tanks provide regulating the frequency for the damping of periodic movement of said body by regulating the passage of the liquid and the air above said liquid through said ducts whereby the frequency and the damping can be adjusted independently of each other.

2. The installation of claim 1 wherein said frequency regulating means is a slide valve.

3. The installation of claim 1 wherein said frequency regulating means is a rotary valve.

4. The installation of claim 1 wherein said frequency regulating duct means is arranged above said bypass duct means and exceeds the liquid level in said partially filled tanks so that a free liquid surface is formed in said frequency regulating duct means while said bypass duct means is below the liquid level.

5. The installation of claim 1 wherein said frequency regulating duct means and said bypass duct means are adjacent to one another and formed to exceed the height of the liquid level in said partially filled tanks so that said liquid forms a free surface in each of said duct means.

6. The installation of claim 1 wherein the length of said bypass means is greater than the length of said frequency regulating duct means.

7. The installation of claim 1 wherein said plate is in the form of a comb.

8. The installation of claim 1 wherein said plate contains at least one perforation.

9. The installation of claim 1 wherein said second valve means is a plate with at least one opening.

10. The installation of claim 1 wherein said second valve means is a slide having at least one opening.

11. A passive stabilizing tank installation for damping the rolling motion of a ship, comprising two partially filled lateral tanks which are connected by ducts for the passage of liquid and of air above the liquid in the tanks, a vertical partition between said tanks extending along a portion of the length of the duct for the passage of the liquid in the direction of movement of the liquid and subdividing the ducts partially into two parallel canals, and adjustable frequency regulating full plate arranged so as to substantially extend into only one of the said canals so as to regulate the frequency of the tank substantially independent of the tank damping, and an adjustable damping regulating plate extending over the total width of the canals and having openings so as to substantially damp the movement of the liquid according to the position of said damping regulating plate in the canals substantially independent of the tank frequency. 

1. A passive stabilizing tank installation for damping components in the movement of a floating body which comprises at least two tanks for holding a liquid which are connected by ducts for passage of said liquid and of air above the liquid in the tanks; a frequency regulating duct means in one of said ducts for regulating the frequency of the liquid in said tanks, said frequency regulating duct means having a first valve means with a plate, and bypass duct means, having a second valve therein for adjusting natural tank damping whereby when said tanks are partially filled with liquid said tanks provide regulating the frequency for the damping of periodic movement of said body by regulating the passage of the liquid and the air above said liquid through said ducts whereby the frequency and the damping can be adjusted independently of each other.
 2. The installation of claim 1 wherein said frequency regulating means is a slide valve.
 3. The installation of claim 1 wherein said frequency regulating means is a rotary valve.
 4. The installation of claim 1 wherein said frequency regulating duct means is arranged above said bypass duct means and exceeds the liquid level in said partially filled tanks so that a free liquid surface is formed in said frequency regulating duct means while said bypass duct means is below the liquid level.
 5. The installation of claim 1 wherein said frequency regulating duct means and said bypass duct means are adjacent to one another and formed to exceed the height of the liquid level in said partially filled tanks so that said liquid forms a free surface in each of said duct means.
 6. The installation of claim 1 wherein the length of said bypass means is greater than the length of said frequency regulating duct means.
 7. The installation of claim 1 wherein said plate is in the form of a comb.
 8. The installation of claim 1 wherein said plate contains at least one perforation.
 9. The installation of claim 1 wherein said second valve means is a plate with at least one opening.
 10. The installation of claim 1 wherein said second valve means is a slide having at least one opening.
 11. A passive stabilizing tank installation for damping the rolling motion of a ship, comprising two partially filled lateral tanks which are connected by ducts for the passage of liquid and of air above the liquid in the tanks, a vertical partition between said tanks extending along a portion of the length of the duct for the passage of the liquid in the direction of movement of the liquid and subdividing the ducts partially into two parallel canals, and adjustable frequency regulating full plate arranged so as to substantially extend into only one of the said canals so as to regulate the frequency of the tank substantially independent of the tank damping, and an adjustable damping regulating plate extending over the total width of the canals and having openings so as to substantially damp the movement of the liquid according to the position of said damping regulating plate in the canals substantially independent of the tank frequency. 